Tears occur when water is produced by the lacrimal gland in the corner of the eye while the oil comes from the 30-40 tiny meibomian glands in the eyelids — its role is to cover the water and prevent it evaporating too quickly. The mucus is made by conjunctival goblet cells on the surface of the eye, and helps bind the water to the eye. This balance of the three components is delicate and if we lack the right amount of one or more, it can lead to ‘unstable tear film’, said Geoffrey Rose recently, a consultant  ophthalmologist at Moorfields Eye Hospital, London. Other studies reveal why men can't cry even if they want to. Testosterone seems to inhibit crying, which may explain why women weep more than men All our tears are controlled by the autonomic nervous system, which regulates body processes including heartbeat and digestion. The parasympathetic side of the nervous system is triggered by emotion, says Professor Chang, causing contractions within the lacrimal gland — the theory is that this helps us relax. We tend to cry most through despair, adds Professor Ad Vingerhoets, a leading researcher in this field. As well as soothing and helping us relax, Professor Vingerhoets says tears help us tell others that we need help. Humans are the only animals to produce emotional tears. People cry more if they have been brought up in a home where crying is more common, adds Professor Vingerhoets. Testosterone seems to inhibit crying, which may explain why women weep more than men. ‘We see this in gender-change operations. Patients report an increase or decrease in crying.’ Too many tears can be a symptom of dry eyes. ‘If you don’t produce enough basal tears, the eyes feel dry so they compensate by triggering the tear gland to make reflex tears, causing a watery eye,’ says Professor Chang. Another cause of excess tears is poor drainage, usually due to the lacrimal punctum (the tiny holes in the corner of the eye) being too small or if there’s a narrowing or blockage of the drainage system inside the nose, caused by infection, inflammation, facial injury or tumours. Watery eyes can also be caused by drooping eyelids, which becomes more common with age, although an injury or Bell’s palsy can also affect the eyelid. ‘As a result the windscreen wiper effect of the eyelids doesn’t function properly and the tears can’t drain into the holes and go inside our nose,’ says Professor Chang.